1. Field of the Invention
The present invention relates to a comparator for comparing levels of a plurality of currents and detecting the order of the levels.
2. Description of the Related Art
It has been difficult to directly compare one current level with another. For this reason, therefore, a plurality of current levels conventionally are converted to corresponding voltage levels by using resistors or the like to compare the current levels. Then, the voltage levels are compared by a voltage comparator. However, according to this method, the current levels change depending on the resistors used. Thus, a current level cannot be determined with greater accuracy.
An article titled "Current-mode algorithmic analog-to-digital converter", IEEE Journal of solid state circuits, vol. 25, No. 4, pp997-1004, 1990, shows circuits for comparing two current levels. FIGS. 1, 4 and 7 of the above article show a circuit which compares two current levels with each other by using a voltage comparator. FIG. 3 of the article shows a basic circuit configuration for comparing two current levels with each other, in which the output current of one current driver is supplied to the other current driver, and the node of the two current drivers is connected to the input terminal of an inverter.
However, according to the arrangement disclosed in this article, the time required for charging and discharging gate capacitances of the inverter is prolonged when two current levels approximate each other. As a result, the operation speed is slow. Further, a through or rush current flows through the inverter, resulting in increased power dissipation.